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Dominic Joyce

Publications and source records attributed to Dominic Joyce.

At least 55 records · Page 3Linked to original sources
arXiv2010

Generalized Donaldson-Thomas invariants

This is a survey of the book arXiv:0810.5645 with Yinan Song. Let X be a Calabi-Yau 3-fold over C. The Donaldson-Thomas invariants of X are integers DT^a(t) which count stable sheaves with Chern character a on X, with respect to a Gieseker stability condition t. They are defined only for Chern characters a for which there are no strictly semistable sheaves on X. They have the good property that they are unchanged under deformations of X. Their behaviour under change of stability condition t was not understood until now. We discuss "generalized Donaldson-Thomas invariants" \bar{DT}^a(t). These are rational numbers, defined for all Chern characters a, and are equal to DT^a(t) if there are no strictly semistable sheaves in class a. They are deformation-invariant, and have a known transformation law under change of stability condition. We conjecture they can be written in terms of integral "BPS invariants" \hat{DT}^a(t) when the stability condition t is "generic". We extend the theory to abelian categories of representations of a quiver with relations coming from a superpotential, and connect our ideas with Szendroi's "noncommutative Donaldson-Thomas invariants" and work by Reineke and others. There is significant overlap between arXiv:0810.5645 and the independent paper arXiv:0811.2435 by Kontsevich and Soibelman.

math.AG↗
arXiv2010

Self-similar solutions and translating solitons for Lagrangian mean curvature flow

We construct many self-similar and translating solitons for Lagrangian mean curvature flow, including self-expanders and translating solitons with arbitrarily small oscillation on the Lagrangian angle. Our translating solitons play the same role as cigar solitons in Ricci flow, and are important in studying the regularity of Lagrangian mean curvature flow. Given two transverse Lagrangian planes R^n in C^n with sum of characteristic angles less than pi, we show there exists a Lagrangian self-expander asymptotic to this pair of planes. The Maslov class of these self-expanders is zero. Thus they can serve as local models for surgeries on Lagrangian mean curvature flow. Families of self-shrinkers and self-expanders with different topologies are also constructed. This paper generalizes the work of Anciaux, Joyce, Lawlor, and Lee and Wang.

math.DG↗
arXiv2008

Kuranishi homology and Kuranishi cohomology

A Kuranishi space is a topological space with a Kuranishi structure, defined by Fukaya and Ono. Kuranishi structures occur naturally on moduli spaces of J-holomorphic curves in symplectic geometry. Let Y be an orbifold and R a commutative ring or Q-algebra. We define two kinds of Kuranishi homology KH_*(Y;R). The chain complex KC_*(Y;R) defining KH_*(Y;R) is spanned over R by [X,f,G], for X a compact oriented Kuranishi space with corners, f : X --> Y smooth, and G "gauge-fixing data" which makes Aut(X,f,G) finite. Our main result is that these are isomorphic to singular homology. We define Poincare dual Kuranishi cohomology, isomorphic to compactly-supported cohomology. We define five kinds of Kuranishi (co)bordism spanned by isomorphism classes[X,f] for X a compact oriented Kuranishi space without boundary and f : X --> Y smooth. They are new topological invariants, and we show they are very large. These theories are powerful new tools in symplectic geometry. Defining virtual cycles and chains for moduli spaces of J-holomorphic curves is trivial in Kuranishi (co)homology. There is no need to perturb moduli spaces, and no problems with transversality. This gives major simplifications in Lagrangian Floer cohomology. We define new Gromov-Witten type invariants in Kuranishi bordism, over Z not Q. We sketch how these may be used to prove the integrality conjecture for Gopakumar-Vafa invariants. This paper is surveyed in arXiv:0710.5634.

math.SG↗
arXiv2008

Kuranishi homology and Kuranishi cohomology: a User's Guide

A Kuranishi space is a topological space with a Kuranishi structure, defined by Fukaya and Ono. Kuranishi structures occur naturally on moduli spaces of J-holomorphic curves in symplectic geometry. This paper is a brief introduction to the author's book arXiv:0707.3572. Let Y be an orbifold and R a Q-algebra. We define the Kuranishi homology KH_*(Y;R) of Y with coefficients in R. The chain complex KC_*(Y;R) defining KH_*(Y;R) is spanned over R by [X,f,G], for X a compact oriented Kuranishi space with corners, f : X --> Y smooth, and G "gauge-fixing data" which makes Aut(X,f,G) finite. Our main result is that KH_*(Y;R) is isomorphic to singular homology. We define a Poincare dual theory of Kuranishi cohomology KH^*(Y;R), isomorphic to compactly-supported cohomology, using a cochain complex KC^*(Y;R) spanned over R by [X,f,C], for X a compact Kuranishi space with corners, f : X --> Y a submersion, and C "co-gauge-fixing data". We also define simpler theories of Kuranishi bordism KB_*(Y;R) and Kuranishi cobordism KB^*(Y;R), for R a commutative ring. These are new topological invariants, and we show they are very large. These theories are powerful new tools in symplectic geometry. Defining virtual cycles and chains for moduli spaces of J-holomorphic curves is trivial in Kuranishi (co)homology. There is no need to perturb moduli spaces, and no problems with transversality. This gives major simplifications in Lagrangian Floer cohomology.

math.SG↗
arXiv2008

Immersed Lagrangian Floer Theory

Let (M,w) be a compact symplectic manifold, and L a compact, embedded Lagrangian submanifold in M. Fukaya, Oh, Ohta and Ono construct Lagrangian Floer cohomology for such M,L, yielding groups HF^*(L,b;Λ) for one Lagrangian or HF^*((L,b),(L',b');Λ) for two, where b,b' are choices of bounding cochains, and exist if and only if L,L' have unobstructed Floer cohomology. These are independent of choices up to canonical isomorphism, and have important invariance properties under Hamiltonian equivalence. Floer cohomology groups are the morphism groups in the derived Fukaya category of (M,w), and so are an essential part of the Homological Mirror Symmetry Conjecture of Kontsevich. The goal of this paper is to extend all this to immersed Lagrangians L in M with immersion i : L --> M, with transverse self-intersections. In the embedded case, Floer cohomology HF^*(L,b;Λ) is a modified, 'quantized' version of cohomology H^*(L;Λ) over the Novikov ring Λ. In our immersed case, HF^*(L,b;Λ) turns out to be a quantized version of the sum of H^*(L;Λ) with a Λ-module spanned by pairs (p,q) for p,q distinct points of L with i(p)=i(q) in M. The theory becomes simpler and more powerful for graded Lagrangians in Calabi-Yau manifolds, when we can work over a smaller Novikov ring Λ_{CY}. The proofs involve associating a gapped filtered A-infinity algebra over Λor Λ_{CY} to i : L --> M, which is independent of nearly all choices up to canonical homotopy equivalence, and is built using a series of finite approximations called A_{N,0} algebras for N=0,1,2,...

math.SG↗
arXiv2007

Configurations in abelian categories. III. Stability conditions and identities

This is the third in a series math.AG/0312190, math.AG/0503029, math.AG/0410268 on configurations in an abelian category A. Given a finite partially ordered set (I,<), an (I,<)-configuration (σ,ι,π) is a finite collection of objects σ(J) and morphisms ι(J,K) or π(J,K) : σ(J) --> σ(K) in A satisfying some axioms, where J,K are subsets of I. Configurations describe how an object X in A decomposes into subobjects. The first paper math.AG/0312190 defined configurations and studied moduli spaces Obj_A, M(I,<)_A of objects and (I,<)-configurations in A, using the theory of Artin stacks. The second math.AG/0503029 considered algebras of constructible functions and "stack functions" on Obj_A, using the theories developed in math.AG/0403305, math.AG/0509722. This paper introduces (weak) stability conditions (t,T,<) on A. We show the moduli spaces Obj_{ss}^a(t),Obj_{st}^a(t) of t-(semi)stable objects in class a in K(A) are constructible sets in the stack Obj_A, and some configuration moduli spaces M_{ss},...,M_{st}^b(I,<,k,t)_A are constructible in M(I,<)_A. So their characteristic functions d_{ss}^a(t),... and d_{ss}(I,<,k,t),... are constructible functions on Obj_A and M(I,<)_A. We prove many identities relating pushforwards of these functions under 1-morphisms between moduli stacks. These encode facts about, for example, the Euler characteristic of the family of ways of decomposing a t-semistable object into t-stable factors, and constitute a kind of "universal algebra of t-(semi)stability". Using these we define interesting (Lie) algebras of constructible functions H^{pa}_t,H^{to}_t and L^{pa}_t,L^{to}_t on Obj_A. All this is generalized to "stack functions".

math.AG↗
arXiv2007

Configurations in abelian categories. IV. Invariants and changing stability conditions

This is the fourth in a series of papers math.AG/0312190, math.AG/0503029, math.AG/0410267 on configurations in an abelian category A. Given a finite partially ordered set (I,<), an (I,<)-configuration is a finite collection of objects and morphisms in A satisfying some axioms. Configurations describe how an object X in A decomposes into subobjects. The first paper math.AG/0312190 defined configurations and studied moduli spaces Obj_A, M(I,<)_A of objects and (I,<)-configurations in A, using the theory of Artin stacks. The second math.AG/0503029 considered algebras of constructible functions and "stack functions" on Obj_A, using the theories developed in math.AG/0403305, math.AG/0509722. The third math.AG/0410267 introduced stability conditions (t,T,<) on A, and showed the moduli space Obj_{ss}^a(t) of t-semistable objects in class a in A is a constructible set in Obj_A, so its characteristic function d_{ss}^a(t) is constructible. It proved many identities on constructible and stack functions such as d_{ss}^a(t). This paper first studies how Obj_{ss}^a(t) changes as we vary the stability condition (t,T,<) to (t',T',<), by writing d_{ss}^a(t') as a sum of products of d_{ss}^b(t). Then we discuss invariants I_{ss}^a(t) or I_{ss}(I,<,k,t) 'counting' t-semistable objects and configurations in A, satisfying identities and transformation laws from (t,T,<) to (t',T',<). We compute the invariants when A is a category mod-KQ of representations of a quiver Q or coh(P) of coherent sheaves on a smooth projective curve P. We find special properties of the invariants when A=coh(P) for P a surface with K_P^{-1} nef, or P a Calabi-Yau 3-fold.

math.AG↗
arXiv2007

Motivic invariants of Artin stacks and 'stack functions'

An invariant I of quasiprojective K-varieties X with values in a commutative ring R is "motivic" if I(X)= I(Y)+I(X\Y) for Y closed in X, and I(X x Y)=I(X)I(Y). Examples include Euler characteristics chi and virtual Poincare and Hodge polynomials. We first define a unique extension I' of I to finite type Artin K-stacks F, which is motivic and satisfies I'([X/G])=I(X)/I(G) when X is a K-variety, G a "special" K-group acting on X, and [X/G] is the quotient stack. This only works if I(G) is invertible in R for all special K-groups G, which excludes I=chi as chi(K*)=0. But we can extend the construction to get round this. Then we develop the theory of "stack functions" on Artin stacks. These are a universal generalization of constructible functions on Artin stacks, as studied in the author's paper math.AG/0403305. There are several versions of the construction: the basic one SF(F), and variants SF(F,I,R),... "twisted" by motivic invariants. We associate a Q-vector space SF(F) or an R-module SF(F,I,R) to each Artin stack F, with functorial operations of multiplication, pullbacks phi^* and pushforwards phi_* under 1-morphisms phi : F --> G, and so on. They will be important tools in the author's series on "Configurations in abelian categories", math.AG/0312190, math.AG/0503029, math.AG/0410267 and math.AG/0410268.

math.AG↗
arXiv2006

Holomorphic generating functions for invariants counting coherent sheaves on Calabi-Yau 3-folds

Let X be a Calabi-Yau 3-fold, T=D^b(coh(X)) the derived category of coherent sheaves on X, and Stab(T) the complex manifold of Bridgeland stability conditions Z on T. It is conjectured that one can define rational numbers J^a(Z) for Z in Stab(T) and a in the numerical Grothendieck group K(T) generalizing Donaldson-Thomas invariants, which `count' Z-semistable (complexes of) coherent sheaves on X in class a, and whose transformation law under change of Z is known. This paper explains how to combine such invariants J^a(Z), if they exist, into a family of holomorphic generating functions F^a:Stab(T) --> C. Surprisingly, requiring the F^a to be continuous and holomorphic determines them essentially uniquely, and implies they satisfy a p.d.e., which can be interpreted as the flatness of a connection over Stab(T) with values in an infinite-dimensional Lie algebra L. The author believes that underlying this mathematics there should be some new physics, in String Theory and Mirror Symmetry. String Theorists are invited to work out and explain this new physics.

hep-th↗
arXiv2006

Configurations in abelian categories. I. Basic properties and moduli stacks

This is the first in a series of papers math.AG/0503029, math.AG/0410267, math.AG/0410268 on "configurations" in an abelian category A. Given a finite partially ordered set (I,<), an (I,<)-configuration (σ,ι,π) is a finite collection of objects σ(J) and morphisms ι(J,K) or π(J,K) : σ(J) --> σ(K) satisfying some axioms, where J,K are subsets of I. Configurations describe how an object X in A decomposes into subobjects, and are especially useful for studying stability conditions on A. This paper defines and motivates the idea of configurations, and explains some natural operations upon them -- subconfigurations, quotient configurations, refinements, improvements and substitution. Then we study moduli spaces of (I,<)-configurations in A, using the theory of Artin stacks. We prove well-behaved moduli stacks exist when A is an abelian category of coherent sheaves or vector bundles on a projective K-scheme P, or of representations of a quiver Q. We define many natural 1-morphisms between the moduli stacks, some of which are representable or of finite type. The sequels will apply these results to construct and study infinite-dimensional algebras associated to a quiver Q, and to define systems of invariants of a projective K-scheme P that "count" (semi)stable coherent sheaves and satisfy interesting identities.

math.AG↗
arXiv2006

Configurations in abelian categories. II. Ringel-Hall algebras

This is the second in a series math.AG/0312190, math.AG/0410267, math.AG/0410268 on configurations in an abelian category A. Given a finite partially ordered set (I,<), an (I,<)-configuration (σ,ι,π) is a finite collection of objects σ(J) and morphisms ι(J,K) or π(J,K) : σ(J) --> σ(K) in A satisfying some axioms, where J,K are subsets of I. Configurations describe how an object X in A decomposes into subobjects. The first paper math.AG/0312190 defined configurations and studied moduli spaces of (I,<)-configurations in A, using the theory of Artin stacks. It proved well-behaved moduli stacks Obj_A, M(I,<)_A of objects and configurations in A exist when A is the abelian category coh(P) of coherent sheaves on a projective K-scheme P, or mod-KQ of representations of a quiver Q. Write CF(Obj_A) for the vector space of constructible functions on Obj_A. Motivated by Ringel-Hall algebras, we define an associative multiplication * on CF(Obj_A) using pushforwords and pullbacks along 1-morphisms between the M(I,<)_A, making CF(Obj_A) into an algebra. We also study representations of CF(Obj_A), the Lie subalgebra CF^ind(Obj_A) of functions supported on indecomposables, and other algebraic structures on CF(Obj_A). Then we generalize these ideas to stack functions SF(Obj_A), a universal generalization of constructible functions on stacks introduced in math.AG/0509722, containing more information. Under extra conditions on A we can define (Lie) algebra morphisms from SF(Obj_A) to some explicit (Lie) algebras, which will be important in the sequels on invariants counting t-(semi)stable objects in A.

math.AG↗
arXiv2006

Constructible functions on Artin stacks

Let K be an algebraically closed field, X a K-scheme, and X(K) the set of closed points in X. A constructible set C in X(K) is a finite union of subsets Y(K) for finite type subschemes Y in X. A constructible function f : X(K) --> Q has f(X(K)) finite and f^{-1}(c) constructible for all nonzero c. Write CF(X) for the Q-vector space of constructible functions on X. Let phi : X --> Y and psi : Y --> Z be morphisms of C-varieties. MacPherson defined a Q-linear "pushforward" CF(phi) : CF(X) --> CF(Y) by "integration" w.r.t. the topological Euler characteristic. It is functorial, that is, CF(psi o phi)=CF(psi) o CF(phi). This was extended to K of characteristic zero by Kennedy. This paper generalizes these results to K-schemes and Artin K-stacks with affine stabilizers. We define notions of Euler characteristic for constructible sets in K-schemes and K-stacks, and pushforwards and pullbacks of constructible functions, with functorial behaviour. Pushforwards and pullbacks commute in Cartesian squares. We also define "pseudomorphisms", a generalization of morphisms well suited to constructible functions problems.

math.AG↗
arXiv2005

Deformations of asymptotically cylindrical coassociative submanifolds with fixed boundary

McLean proved that the moduli space of coassociative deformations of a compact coassociative 4-submanifold C in a G_2-manifold (M,phi,g) is a smooth manifold of dimension equal to b^2_+(C). In this paper, we show that the moduli space of coassociative deformations of a noncompact, asymptotically cylindrical coassociative 4-fold C in an asymptotically cylindrical G_2-manifold (M,phi,g) is also a smooth manifold. Its dimension is the dimension of the positive subspace of the image of H^2_cs(C,R) in H^2(C,R).

math.DG↗
arXiv2005

Configurations in abelian categories. II. Moduli stacks

This paper has been withdrawn, because I have merged it with paper I of the series, math.AG/0312190. The main results of this paper now appear in sections 7-9 of the revised version of math.AG/0312190, with shortened and improved proofs.

math.AG↗
arXiv2004

The exceptional holonomy groups and calibrated geometry

The exceptional holonomy groups are G2 in 7 dimensions, and Spin(7) in 8 dimensions. Riemannian manifolds with these holonomy groups are Ricci-flat. This is a survey paper on exceptional holonomy, in two parts. Part I introduces the exceptional holonomy groups, and explains constructions for compact 7- and 8-manifolds with holonomy G2 and Spin(7). The simplest such constructions work by using techniques from complex geometry and Calabi-Yau analysis to resolve the singularities of a torus orbifold T^7/G or T^8/G, for G a finite group preserving a flat G2 or Spin(7)-structure on T^7 or T^8. There are also more complicated constructions which begin with a Calabi-Yau manifold or orbifold. Part II discusses the calibrated submanifolds of G2 and Spin(7)-manifolds: associative 3-folds and coassociative 4-folds for G2, and Cayley 4-folds for Spin(7). We explain the general theory, following Harvey and Lawson, and the known examples. Finally we describe the deformation theory of compact calibrated submanifolds, following McLean.

math.DG↗
arXiv2004

U(1)-invariant special Lagrangian 3-folds I. Nonsingular solutions

This is the first of three papers math.DG/0111326, math.DG/0204343 studying special Lagrangian 3-submanifolds (SL 3-folds) N in C^3 invariant under the U(1)-action (z_1,z_2,z_3) --> (gz_1,g^{-1}z_2,z_3) for unit complex numbers g, using analytic methods. The three papers are surveyed in math.DG/0206016. Let N be such a U(1)-invariant SL 3-fold. Then |z_1|^2-|z_2|^2=2a on N for some real number a. Locally, N can be written as a kind of graph of functions u,v : R^2 --> R satisfying a nonlinear Cauchy-Riemann equation depending on a, so that u+iv is like a holomorphic function of x+iy. When a is nonzero, u,v are always smooth and N is always nonsingular. But if a=0, there may be points (x,0) where u,v are not differentiable, which correspond to singular points of N. This paper focusses on the nonsingular case, when a is nonzero. We prove analogues for our nonlinear Cauchy-Riemann equation of well-known results in complex analysis. In particular, we prove existence and uniqueness for solutions of two Dirichlet problems derived from it. This yields existence and uniqueness of a large class of nonsingular U(1)-invariant SL 3-folds in C^3, with two kinds of boundary conditions. In the sequels we extend these results to the singular case a=0. The next paper math.DG/0111326 proves existence and uniqueness of continuous weak solutions to the two Dirichlet problems when a=0. This gives existence and uniqueness of a large class of singular U(1)-invariant SL 3-folds in C^3, with boundary conditions. The final paper math.DG/0204343 studies the nature of the singularities that arise, and constructs U(1)-invariant special Lagrangian fibrations of open sets in C^3.

math.DG↗
arXiv2004

U(1)-invariant special Lagrangian 3-folds II. Existence of singular solutions

This is the second of three papers math.DG/0111324, math.DG/0204343 studying special Lagrangian 3-submanifolds (SL 3-folds) N in C^3 invariant under the U(1)-action (z_1,z_2,z_3) --> (gz_1,g^{-1}z_2,z_3) for unit complex numbers g, using analytic methods. The three papers are surveyed in math.DG/0206016. If N is such a 3-fold then |z_1|^2-|z_2|^2=2a on N for some real number a. Locally, N can be written as a kind of graph of functions u,v : R^2 --> R satisfying a nonlinear Cauchy-Riemann equation depending on a, so that u+iv is like a holomorphic function of x+iy. The first paper math.DG/0111324 studied the case when a is nonzero. Then u,v are smooth and N is nonsingular. It proved existence and uniqueness for solutions of two Dirichlet problems derived from the equations on u,v. This implied existence and uniqueness for a large class of nonsingular U(1)-invariant SL 3-folds in C^3, with boundary conditions. In this paper and its sequel math.DG/0204343 we focus on the case a=0. Then the nonlinear Cauchy-Riemann equation is not always elliptic. Because of this there may be points (x,0) where u,v are not differentiable, corresponding to singular points of N. This paper is concerned largely with technical analytic issues, and the sequel with the geometry of the singularities of N. We prove a priori estimates for derivatives of solutions of the nonlinear Cauchy-Riemann equation, and use them to show existence and uniqueness of weak solutions u,v to the two Dirichlet problems when a=0, which are continuous and weakly differentiable. This gives existence and uniqueness for a large class of singular U(1)-invariant SL 3-folds in C^3, with boundary conditions.

math.DG↗